Active noise control systems are well known. One application for such system is on automotive vehicles. It is possible for engine noises to be propagated through the air intake manifold in a manner that they are heard in the passenger compartment of the vehicle. Typical active noise control systems include a speaker for generating a noise canceling signal. The speaker produces a sound that is out of phase with the engine noise to cancel out the noise to reduce the possibility for it being heard in the passenger compartment.
Typical active noise control systems require information from the vehicle engine for determining the control state and parameters and for computing the necessary speaker output in real time. When true cancellation is desired, very accurate information is required. Such information is acquired in some circumstances through the vehicle databus or by directly taking analog signals from various transducers.
The precise information for noise cancellation provides an indication abut the phase of the induction sound. Other vehicle parameters need to be predicted accurately, such as engine crank position, rotational speed, throttle opening, temperature, etc. The phase of the induction sound is sensitive to all such parameters.
At a minimum, the engine rotational speed and throttle opening position are required for any useful noise attenuation. Conventional systems rely upon at least two sensors for such information.
Accordingly, multiple inputs to the active noise control system typically are required. When analog signals are used, that adds cost and complexity to the system. When digital signals from the vehicle data bus are used, that adds complexity to the system. Either of these options require relatively significant interfacing with existing vehicle electronics.
Such noise control systems have not been able to be marketed in an after-market product because they require a significant interface with existing vehicle electronics. After-market products that require integrating with other vehicle electronics in that manner are not practical.
There is a need for a system that is not so complex or expensive. Additionally, it would be beneficial to provide a system that can be sold as an after-market product to provide noise control capabilities. This invention addresses that need while avoiding the shortcomings and drawbacks associated with typical systems.